1. Field of the Invention
The present invention relates to a fixing apparatus used in an image forming apparatus such as an electrophotographic copying machine, and more particularly, it relates to a fixing apparatus having an improved cleaning member for cleaning a fixing rotary member of the fixing apparatus.
2. Related Background Art
In image forming apparatuses such as electrophotographic copying machines, as a last finishing step of an image forming process, a non-fixed image transferred to a recording material (for example, a paper sheet or an OHP sheet) is permanently fixed to the recording material. To this end, a fixing apparatus of a heat roll fixing type is generally used.
As shown in FIG. 7, a conventional fixing apparatus of a heat roll fixing type comprises a fixing device 10 of a heat roll fixing type and a cleaning device 20. The fixing device 10 includes a fixing roller 1 formed of a silicone rubber layer 3 having a predetermined thickness coated on an aluminium core cylinder 2, a pressure roller 4 constituted by a silicone rubber layer 6 having a predetermined thickness coated on an aluminium core cylinder 5 and a resin coating layer 6a disposed on the silicone rubber layers and heat sources 7 disposed within the fixing roller 1 and the pressure roller 4. A surface temperature of the fixing roller 1 is maintained at about 170.degree. C. by heat from its heat source 7 and transmission of heat from the pressure roller 4.
According to the fixing apparatus having the above-mentioned construction, when a recording material 13 to which a non-fixed toner image 12 was transferred is sent to the fixing apparatus by a convey means (not shown), while the recording material is being passed through a nip between the fixing roller 1 and pressure roller 4 of the fixing device 10, the non-fixed toner image 12 is thermally fixed onto the recording material 13 by the fixing roller 1. In this case, a small amount of toner forming the non-fixed toner image on the recording material 13 is transferred (offset) to the surface of the fixing roller 1. When the toner is offset to the fixing roller 1, since there is a danger of smudging an electrophotographic image (i.e., worsening image quality) due to the offset toner, the surface of the fixing roller 1 is cleaned by the cleaning device 20.
Although various kinds of cleaning devices can be used as the cleaning device 20 shown in FIG. 7, a cleaning device in which a web 15 formed from fibers is contacted with the surface of the fixing roller 1 and the cleaning of the fixing roller 1 is effected by shifting the web 15 while contacting with the fixing roller is known (for example, refer to Japanese Patent Laid-Open Application No. 50-57237). Explaining in more detail, the cleaning device 20 comprises a web supply shaft 21, a web take-up shaft 22 and a hold-dowry roller 23. The web 15 is supplied from the supply shaft 21 and is wound around the take-up shaft 22; meanwhile, the web 15 is urged against the surface of the fixing roller 1 by the hold-down roller 23, thereby cleaning the fixing roller. An urging force of the hold-down roller 23 for urging the web 15 against the fixing roller 1 is adjusted by a pressurizing means such as a spring 24. The web 15 is shifted in a direction shown by the arrow C and is wound around the take-up shaft 22 by means of a driving device (not shown) for driving the take-up shaft 22. Incidentally, in FIG. 7, the reference numeral 16 denotes a mold releasing agent coating device for coating mold releasing agent such as silicone oil on the surface of the fixing roller 1 by means of a coating member 18
In the above web 15 formed from the fibers, since the toner scraped from the surface of the fixing roller 1 is absorbed between the fibers, the toner can be removed from the fixing roller efficiently, thereby providing high cleaning ability. However, since the fiber cloth of the web 15 is formed from Nomex (tradename: manufactured by Du Pont) there are the following disadvantages.
Nomex is obtained by weaving aramid fibers made of aromatic polyamide with polyester fibers and binding the aramid fibers and the polyester fibers to each other by heat. In the cleaning operation, due to the heat from the fixing roller 1 contacting with the web 15, the aramid fibers are softened to lose rigidity. Consequently, toner scraping ability (obtained by "fiber rigidity") of the aramid fibers is worsened, so that the toner offset on the fixing roller 1 passes through the softened aramid fibers in the web 15 not to clean the fixing roller 1 adequately.
Of course, even when the rigidity of the aramid fibers in the web 15 is lost to worsen the scraping ability, if an amount of the offset toner is small, the toner can be cleaned from the fixing roller 1 by the web 15. However, as the amount of offset toner is increased due to degradation of the fixing roller 1, the influence of the reduction of the scraping ability of the aramid fibers becomes noticeable, so that the toner cannot be removed from the fixing roller 1 adequately by the web 15, to thereby cause poor cleaning. Consequently, as the fixing roller 1 is further rotated, the offset toner still remaining on the fixing roller 1 is contacted with and transferred to the pressure roller 4 and/or the succeeding recording material, to thereby smudge the pressure roller and/or the recording material.
To avoid this, in the conventional techniques, PPS fibers which are not softened by heat were used as shown in Japanese Patent Laid-Open Application No. 3-183284, or, a web was metal-plated to increase rigidity of the web itself as shown in Japanese Patent Laid-Open Application No. 2-83691. These proposals increase the toner scraping ability. However, fundamentally, the fixing roller is constructed mainly in consideration of its mold releasing ability. Thus, since the surface of the fixing roller is constructed by relatively soft silicone rubber and the like, when the web having great rigidity is slidingly contacted with the fixing roller, the roller surface is damaged. That is to say, due to unevenness In fibers of the web itself and/or the plated metal foils on the web, a large number of scratches are formed on the surface of the fixing roller along its circumferential direction, which cause deterioration of image quality and shorten the service life of the fixing roller.